The use of short fibres of a fibre length of some micrometres up to two or more millimetres in polymer compositions is frequently restricted or impossible because the fibres cannot adequately be incorporated or dispersed in the polymer matrix. This particularly applies to some types of high performance fibres, such as aramid fibres or aramid fibre pulp.
The short fibres or pulps to be used are conventionally in the form of tangled, wadding-like bundles which, using conventional mixing methods, cannot be incorporated and distributed in a polymer matrix, in particular elastomer compositions, or only incompletely so.
In the past, various processes have been developed for finishing fibres in order to improve the incorporability of the fibres. Thus, for example, masterbatches of various polymers are produced in mixing equipment with the addition of further auxiliary substances, as well as fibres.
A disadvantage of the process is that it does not ensure complete wetting and dispersion of the fibres (disentanglement of the fibre tangles), resulting in so-called fibre nests in the polymer.
WO 94/24 193 (PCT/US 94/03991) describes the production of a masterbatch using solvents. The polymer is dissolved in up to 4 times its quantity of solvent. The fibres are then introduced into up to 20 times their quantity of this solution. The solvent is then evaporated off. The polymer remains behind on the fibre. If the quantity of solvent is sufficiently large (at least 50% of the introduced quantity of fibre), a masterbatch is then obtained.
A disadvantage of this process is that the polymer must first be dissolved in large quantities of solvent so that the fibres may then be absorbed therein. The solvent must then be evaporated off again. This makes little economic or environmental sense.